Abstract Out-of-hospital cardiac arrest (OHCA) is a major cause of death in the US, affecting over 300,000 citizens annually. The Institute of Medicine (IOM) recently released ?Strategies to Improve Survival from Cardiac Arrest: A Time to Act,? stating ?although breakthroughs in understanding and treatment are impressive, the ability to consistently deliver timely interventions and high-quality care is less than impressive.? The IOM?s work highlighted that the cooperation between stakeholders essential to deliver optimal care for patients with OHCA is lacking. Indeed, marked geographic variability exists in the management and outcomes of OHCA, and leading professional societies support the development of cardiac arrest systems of care. OHCA survival in a given community is a function of its individuals (e.g. age, comorbid conditions), hospital characteristics (e.g. protocols for targeted temperature management and early cardiac catheterization), and organization of the system of care (e.g. percent of patients taken to high volume centers). In the current structure, accountability for outcomes resides at the provider or facility level, but no regional benchmarks or incentives exist to improve OHCA outcomes at the community level. The IOM defines total population health as ?the health of all persons living in a specified geopolitical area? and encourages health systems, hospitals, and payers to create systems of care that meet the needs of patients and improve the health of the total population. The proposed study develops a new attribution method for Medicare beneficiaries sustaining OHCA by applying spatial methods to identify naturally occurring geographic clusters defined not by health system affiliation, but by how patients access healthcare for emergencies. Defining regional boundaries allows for benchmarking of outcomes, and facilitates development of population-based incentives. This approach can be directly translated into practice by using population-based payment strategies as described by the U.S. Secretary of Health & Human Services and implemented by the Centers for Medicare & Medicaid Services. Aim 1 will describe the existing patterns of hospital utilization for patients with OHCA. Aim 2 will identify existing spatial clusters of hospitals that treat members of a community with OHCA. Aim 3 will determine variability in risk-adjusted outcomes at the population level. This work provides the scaffolding to enable the construction of new payment models that are consistent with the IOM vision of total population health, the American Heart Association?s efforts to build regional systems of care, and the CMS efforts to improve population health. Our research team, richly experienced in health services research methods and application to cardiac arrest investigations, is uniquely positioned to conduct these studies, which will build on our current work under an R56 mechanism.